Inspection and Verification (Start Testing Here)

Preliminary Checks
- A loss of power, lack of power or no start condition may be diagnosed as an exhaust restriction caused by a plugged catalytic converter. A plugged catalytic converter (internal deterioration) is usually caused by abnormal engine operation upstream of the catalyst. Events that produce higher than normal temperatures in the catalyst are particularly suspect.

Actions

- Perform the following diagnostics to confirm that the catalytic converter is the root cause of the customer's complaint.

- Visually inspect the engine compartment wiring harness and connectors for damage. Check wire harness insulation for burns and scrapes, etc. Check for loose or broken connectors. Also ensure that vacuum hoses are properly routed and securely connected. Service as necessary.


The following is a list of items that should be checked in the event of a catalyst internal failure (internal failure also includes noise caused by loose internal components):

- HO2S - Fuel pressure
- Spark timing - Throttle body and linkage
- Secondary ignition - Secondary Air Injection (AIR) System

WHY AND HOW EACH OF THE ITEMS SHOULD BE CHECKED IS DISCUSSED BELOW.

HO2S
- Incorrect HO2S signal input to the Powertrain Control Module (PCM) (i.e. rich / lean input signal when the engine is operating under lean / rich conditions) may cause an abnormal temperature increase in the catalyst.

- Check for HO2S Diagnostic Trouble Code (DTC):

- Refer to Powertrain Management/Testing and Inspection/Flow of Diagnosis/Procedures/Diagnostic Routines and follow Quick Test directions in the Diagnostic Routines, and enter the Key On Engine Off (KOEO) and Key On Engine Running (KOER) Self-Test. Service any DTC generated according to Quick Test directions. If any HO2S DTCs are generated, be sure to check for proper HO2S ground during HO2S testing. Service as necessary.

Additional areas that should be checked if the HO2S ground is good:
- Ignition coil - Fuel contain
- Air filter - Manifold leaks (intake or exhaust)
- Stuck open fuel injector - Poor power ground
- Engine above normal operating temperature, (check thermostat and coolant level)

Spark Timing
- Spark timing that is retarded below specification may increase the exhaust gas temperature and shorten catalyst life.

Check Spark Timing
- Check base timing with SPOUT disconnected (if applicable), on most vehicles, base timing is not adjustable. Set base to the value indicated on the vehicle emissions control information decal. Reconnect the SPOUT connector. Check computed timing with SPOUT connected. Computed timing should equal base timing plus 20 degrees BTDC, + 3 degrees.

Secondary Ignition
- Spark plugs that misfire may allow unburned fuel mixed with air to pass through to the catalyst. The mixture may cause higher than normal catalyst temperatures.

Check Secondary Ignition
- Install engine analyzer on vehicle and check for secondary ignition misfire. Also check spark plugs, spark plug wires, spark plug wire routing and connections, distributor, cap and rotor, etc. Service as necessary.

Fuel Pressure
- Fuel pressure above specification may produce an abnormally rich air/fuel mixture. The rich air/fuel mixture may cause higher than normal catalyst temperatures.

Check Fuel Pressure
- Install fuel pressure gauge. Start and run the engine at idle. Fuel pressures between 28 and 34 psi are expected. Disconnect and inspect the vacuum hose going to the fuel pressure regulator for raw fuel. As a result of disconnecting the vacuum hose, the fuel pressure should rise as high as 40 psi + 3 psi. Fuel pressures above these values should be corrected. However, this may not be the root cause of the concern.

Throttle Body and Linkage
- Throttle plates that do not return to their proper closed position may cause excessive catalyst temperatures during downhill grades.

Check Throttle Body and Linkage
- Visually inspect for binding or sticking throttle linkage, tight speed control linkage or cable, electrical harness and vacuum hose interference, etc. Aftermarket governors or throttle linkage and cables associated with power take-off units may also interfere with proper throttle return. Service as necessary.

Secondary Air Injection (AIR) System
- An AIR system that fails to dump secondary air to atmosphere properly or fails to dump secondary air at the correct time can cause abnormally high catalyst temperatures.

Check AIR System
- Perform a component function check on the AIRD valve, AIRB solenoid, check valves and silencer and filter. Also inspect hoses for damage.

- Verify that the condition is not caused by any of the areas above, then proceed with diagnosis using the procedure starting at B1.

All Other Applications
- A restricted or blocked exhaust system usually results in loss or lack of power. Verify that the condition is not caused by ignition or timing problems, then proceed with diagnosis using the following procedure.